Atomic Force Microscope Image-E. Coli

This image of the common Eschericia coli--or E. coli--was taken using a special microscope called an Atomic Force Microscope (AFM). The AFM image was produced by tracking across the top of the bacteria with a very sharp tip. The tip is as sharp as a few atoms. The very small change in height (amplitude) of the bacteria's surface is electronically amplified and sent to a computer that assembles the image.

Credit: Image by Dee Hartung; from Arizona State University's School of Life Sciences Ask a Biologist website.

Scientists at the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health, have shown how the O157:H7 strain of Escherichia coli causes infection and thrives by manipulating the host immune response. The bacterium secretes a protein called NleH1 that directs the host immune enzyme IKK-beta to alter specific immune responses. This process not only helps the bacterium evade elimination by the immune system, it also works to prolong the survival of the infected host, enabling the bacterium to persist and ultimately spread to unaffected individuals. This finely balanced mechanism, observed in both laboratory and animal models, could be relevant to other pathogens involved in foodborne diseases.

While most E. coli strains help check the growth of harmful bacteria in the guts of animals and humans, a few E. coli strains, such as O157:H7, can cause severe diarrhea, abdominal cramps and, in rare cases, death. Human cases of E. coli O157:H7 have been linked to consumption of raw, undercooked, or spoiled meat.

NIAID researchers plan to use the new information to further study how the host immune system mounts a response to E. coli O157:H7 when infection begins and how the bacterium selectively blocks these defenses. Several foodborne pathogens, including Shigella and Salmonella, use a similar secretion system to disrupt host immune responses and infect gut cells.